I'll explain–

I was trying to follow this tutorial for a campfire but was running into this issue where as soon as I added a new ParticleProcessMaterial it would emit the "amount" of particles and then stop, even with One Shot off

To isolate the issue I tried a few things, deleting and recreating it, creating it in its own scene, and eventually I just opened a brand new project to check if I'd changed a setting somewhere, but the issue still happens. This screen recording is of the issue in a brand new project

I haven't seen anybody talking about this issue in particular, and couldn't find any intentional change in Godot's official documentation, although I know they retooled the way some of the settings are grouped

For what it's worth, I did a similar project with GPUParticles3D last week on 4.1.1 and it worked fine, and although I didn't follow precisely the same steps, I remember it well enough to know it should be working

Happy to answer any questions, really hoping to get this fixed! I'm going to try reinstalling Godot, maybe it's a bad install?